Such circuit arrangements are used for a very wide range of purposes, for example including resonance labels. Such resonance labels, which are used in particular for goods security, for example in department stores, should for obvious reasons be capable of being attached to all possible goods as simply as possible and should therefore be as flat and flexible as possible without their characteristic electrical properties suffering as a result. Attempts have therefore been made to mount the conductor tracks on as thin a layer as possible, which serves both as a support substrate and as an insulating substrate. The conductor tracks are etched in a known manner from a conductive foil or stamped onto the support substrate.
Photo etching techniques, including the screen printing techniques also used in some cases, are relatively expensive, especially because of the complexity of the production process, and are unacceptable from the ecological point of view, since etch sludge is obtained as a non-reusable disposable product. A possible alternative is to stamp conductor tracks onto a support substrate. Thus, U.S. Pat. No. 3,678,577 describes a process in which the conductor tracks are stamped onto a support substrate, very specific properties being required for the substrate materials used.
In a conventional process corresponding to the hot-stamping technique (mentioned in EP-B1-0063347), conductor tracks are applied to a plastic substrate. A conductor foil is applied, together with a support film, to a substrate and is pressed onto the substrate by means of heated die, only the conductor tracks being sheared off and at the same time bonded to the substrate. The support film remains intact and is used for peeling off those parts of the conductor foil which have not been stamped. It is evident that, when the conductor track is stamped into the substrate, this support film must on no account be sheared off also, since otherwise either the support film alone or non-stamped conductor track paths or both will be incompletely removed. Since, in this process, the conductor tracks are slightly embedded in the surface of the substrate, this requirement can be met only by very special support film materials. Furthermore, the substrate must be at least twice as thick as the conductor layer itself, particularly when a further conductor track arrangement is to be provided on the back of the substrate.
In the process described in EP-A1-292827 for the production of a label carrying an oscillating circuit, the conductor tracks are stamped from the conductor foil in two steps. In a first step, a middle track region is stamped out and is covered with an insulating tape. The outer track regions, which accordingly are not covered are stamped out in a second step. This laminate of stamped and partially covered conductor tracks is then mounted on a top film for stabilization. The problem here is the double stamping process, which must be controlled very precisely to ensure that there are no discontinuities in the completely stamped conductor tracks. Covering of the middle track region must also be carried out just as correctly. On the one hand, the insulating tape should not also be stamped but on the other hand, for stabilization, should cover the entire middle conductor tape which has already been stamped out.
DE-A1-3732825 also describes a process in which conductor tracks are stamped from a conductor foil, wherein one part of the stamped foil is pressed onto an adhesive web provided with a mask and the other part of the stamped foil is lifted off from another adhesive web provided with a mask. This process is suitable in particular for simple, complementary circuit patterns, but the masking operations tend to be disadvantageous since the masking must correspond exactly to the conductor track pattern and must do so with very highly defined positive tolerance in order to allow the stamped conductor track to be lifted off satisfactorily. This means, in particular, that multiply wound conductor coils will have a certain minimum width.
In the production of circuit arrangements by the known processes in which conductor tracks are applied to a support film, for example by hot-stamping or stamping, the cross-section of the support film is at least partially changed, there being either a reduction in the thickness due to the stamping in or embossing of the conductor tracks or as a result of the application of additional layers, for example marking agents, the conductor tracks or distortion or warping of the support film in the regions adjacent to the applied conductor tracks.